Buffer tubes are used in the construction of fiber optic cables to house and protect the optical fibers. Typically, these tubes are filled with a hydrocarbon gel or grease to suspend and protect the fiber from water/moisture, and they have stringent requirements for high crush resistance, resistance to micro-bending, low brittleness temperature, good grease compatibility, impact resistance and low post-extrusion shrinkage. Materials used in the manufacture of the buffer tubes include polybutylene terephthalate (PBT), high crystallinity polypropylene(PP) modified for impact resistance, and to a lesser extent, high density polyethylene (HDPE). PBT is a high cost material and cable manufacturers are looking for cost-effective alternatives.
PP as a material for use in buffer tube construction is a market trend in the fiber optical cable field because of its desirable mechanical properties and cost advantage. PP has better flexibility than PBT, and it is easier to use during installation of the cable. High crystallinity PP modified with an elastomer phase has been proposed in the past but further improvements are still desired, such as grease resistance and high excess fiber length (EFL) which is related to the large post shrinkage. Another issue associated with the utilization of PP is that stress whitening can occur when PP is mechanically deformed. Such deformation causing whitening can occur during installation of the optical cable. Accordingly, a need exists for PP buffer tubes that have reduced stress whitening.
U.S. Pat. No. 8,824,845 B1 teaches a method for reducing buffer tube stress whitening by constructing the buffer tube from a composition that comprises (1) at least about 80 weight percent homopolymer polypropylene and/or polypropylene copolymer, and (2) between 100 and 10,000 parts per million (ppm) titanium dioxide.
WO 2010/076231 teaches a cable layer comprising a propylene polymer composition comprising (a) a polypropylene, (b) an elastomeric copolymer comprising units derived from propylene and ethylene and/or C4 to C20 α-olefin, and (c) a polar ethylene polymer, wherein the propylene polymer composition has a gel content of equal or more than 0.20 wt %.
US 2011/0313108 A1 teaches a composition comprising (A) polypropylene, (B) polyethylene, and (C) at least one crystalline block composite comprising (1) a crystalline ethylene based polymer, (2) a crystalline alpha-olefin based polymer, and (3) a block copolymer comprising a crystalline ethylene block and a crystalline alpha-olefin block.